It is said that consuming the flesh of a mermaid confers immortality. This certainly proved to be the case for the 500-year-old Yuta and his friend Mana. However, most people who try to become immortal either die or transform into monsters.

Fifty-five years ago, Towa Kannagi was given mermaid blood by her sister, Sawa, in order to cure a fatal illness. Now, Towa maintains her youthful appearance, save her white hair and beastly arm. For years she has dreamed of restoring her body, resorting to blood transfusions from youthful corpses aided by the local doctor, Shiina.

Mana, mistaken for dead by Shiina, is brought in to have her blood used by Towa. When she discovers that Mana is alive, what lengths will Towa go to in order to restore herself? Will Yuta be able to save Mana in time?